Adhesives have been widely used in various industries for many years, and numerous adhesives are commercially available. But finding a suitable commercially available adhesive to meet certain requirements is not always possible. In some cases, a suitable adhesive can be designed to meet particular specifications, and can take advantage of the availability of new monomers, additives, curing agents and new advanced in polymer processing technology.
Curable adhesives are well known. These include adhesives that are curable by radiation generally, as well as those that are curable by ultraviolet or visible light in particular. Unfortunately, known curable adhesives may suffer from a number of disadvantages. For example, many adhesives suffer from insufficient adhesion and/or inappropriate refractive index to match the refractive indices of the intended substrates. Many adhesives have a refractive index (RI) that is lower than 1.60, which is not suitable for lenses (e.g., electro-active lenses or composite lenses) made of plastic materials having an RI of 1.67 or higher. While there are a few adhesive compositions with high RI, they suffer from poor adhesion, unsuitable viscosity, or poor batch life. Some adhesives also require the use of solvents that must be evaporated during curing, and thus are not suitable for one or more electro-active assembly processes.
A need therefore exists for curable adhesives, especially UV curable adhesives, that exhibit a high RI, and preferably improved adhesion and viscosity.